A TD-SCDMA system is subjected to many kinds of interference, which may be classified into intra-system interference and extra-system interference in terms of an interference source. Most of extra-system interference comes from various communication devices in which transmission of other signals has a period, such as microwave transmission, a mobile television, and civilian and police antennas. A communication device leaks part of power to a frequency band of the TD-SCDMA system, thereby causing interference with the TD-SCDMA system. The extra-system interference affects the TD-SCDMA system slightly, and may affect only a coverage area of several devices. The intra-system interference is mainly caused by a GPS timing offset or interference of a remote base station. The GPS timing offset may be caused by a fault of a device, while the interference of the remote base station is an unavoidable problem for all time division mobile communication systems. The remote base station refers to a base station that is far from the TD-SCDMA system and in which a signal may be neglected theoretically.
FIG. 1 is a schematic diagram of a frame structure of an existing TD-SCDMA system. A TD-SCDMA frame includes: DwPTS (Downlink Pilot Time slot, downlink pilot time slot), UpPTS (Uplink Pilot Time slot), and GP (Guard Period) special time slots, and TS0-TS6 normal time slots. The DwPTS and UpPTS are used as uplink synchronization and downlink synchronization respectively, and do not bear user data. The GP is used as propagation delay guard in an uplink synchronization establishment process, and TS0-TS6 are used to bear user data or control information. In FIG. 1, only TS0 and TS1 are schematically shown for normal time slots. In the TD-SCDMA system, the length of each frame is 10 ms, one 10 ms frame is divided into two sub-frames with completely the same structure, each sub-frame has a time length of 5 ms, and each sub-frame is further divided into seven normal time slots each with a length of 675 μs and three special time slots. A guard interval GP (Guard Period) for downlink-to-uplink switching is 75 μs, and when it is converted to a space transmission distance of a signal, the space transmission distance is 22.5 km, and a cell radius corresponding to the distance is 11.25 km. For interference between base stations, a corresponding interference distance for synchronized base stations is 22.5 km.
It can be seen from the frame structure of the TD-SCDMA system that, after reaching a target base station after a propagation delay, TS0 and DwPTS of a base station at a distance of more than 22.5 km may cause interference with an UpPTS and even an uplink service time slot of the target base station. Moreover, a large number of remote base stations exist in some cases, and therefore their interference cannot be neglected.
FIG. 2 is a schematic diagram showing that a frame of an interfering base station reaches an interfered base station after different delays. Due to different distances and delays, finally generated interference affects different areas.
As shown in FIG. 2, when a signal of the interfering base station reaches the interfered base station after a delay of time t1, a downlink pilot time slot DwPTS of the interfering base station only causes interference with a GP of the interfered base station, and does not cause interference with an UpPTS of the interfered base station at this time. When the signal of the interfering base station reaches the interfered base station after a delay of time t2, the downlink pilot time slot DwPTS of the interfering base station causes interference with both the GP and the UpPTS of the interfered base station, and does not cause interference with TS1 of the interfered base station. When the signal of the interfering base station reaches the interfered base station after a delay of time t3, the DwPTS of the interfering base station causes interference with TS1 of the interfered base station.
Generally, attenuation of signal propagation between base stations is greater than loss of propagation in free space, and a signal has already been attenuated below a noise floor in a distance protection range that corresponds to a GP. However, in a macro cell, propagation manners of a wireless signal around a 2 GHz frequency band in space mainly include free space propagation, troposcatter, diffraction of a wireless signal, and so on. Under a certain meteorological condition, due to influence of atmospheric refraction, a propagation path of an electromagnetic wave that is propagated in a surface layer bends towards the earth's surface. When a curvature exceeds a curvature of the earth's surface, the electromagnetic wave may partially propagate in a thin atmospheric layer with a certain thickness, just like the electromagnetic wave propagates in a metallic waveguide, and this phenomenon is referred to as atmospheric duct propagation of the electromagnetic wave. At this time, a wireless signal that passes through a waveguide causes interference with an uplink pilot time slot UpPTS after a GP and even with TS1 and TS2 time slots of an uplink signal. Interference superposition of a large number of remote base stations is random strong interference, and the strength may be tens of dBs higher than a noise floor. The interference strength may be −100 dBm to −80 dBm for the TD-SCDMA system.
When a downlink pilot time slot DwPTS interferes with an uplink pilot time slot UpPTS, synchronization of an uplink signal of a user may be affected. When interference is large, detection failures of an UpPCH (Uplink Pilot Channel) increase, which may even interfere with an uplink time slot, so that the user cannot perform access. Moreover, such interference has certain randomness and unpredictability, which causes a difficulty in positioning of the interference. Therefore, accurately positioning an interference source so as to take a proper measure for the interference source to avoid interference of the interference source with an uplink signal is an urgent technical problem to be solved.